Recently, in optical communications, research and development of the optical wavelength division multiplexing (WDM) transmission systems have been conducted actively for the way to dramatically increase the transmission capacity thereof, and practical applications have been proceeding. The optical wavelength division multiplexing transmission systems are that a plurality of lights having a wavelength different from each other is wavelength-multiplexed and is transmitted, for example. In such optical wavelength division multiplexing transmission systems, lights need to be demultiplexed at every wavelength from the transmitted multiplexed lights on the light receiving side. On this account, the optical wavelength division multiplexing transmission systems are provided with optical devices that only transmit predetermined optical wavelengths.
One example of the optical devices is an arrayed waveguide grating (AWG) of a planar lightwave circuit (PLC), as shown in FIG. 4. The arrayed waveguide grating is that a waveguide forming area 10 made of silica-based glass is formed on a silicon substrate 1, for example. On the waveguide forming area 10 of the arrayed waveguide grating, the waveguide configuration as shown in the same drawing is formed of cores.
The waveguide configuration of the arrayed waveguide grating is formed to have one or more of optical input waveguides 2 arranged side by side; a first slab waveguide 3 connected to the output ends of the optical input waveguides 2; an arrayed waveguide 4 made of a plurality of channel waveguides 4a arranged side by side, the channel waveguides connected to the output end of the first slab waveguide 3; a second slab waveguide 5 connected to the output end of the arrayed waveguide 4; and a plurality of optical output waveguides 6 arranged side by side, the optical output waveguides connected to the output end of the second slab waveguide 5.
The channel waveguides 4a are a set for propagating lights that have been lead through the first slab waveguide 3 and are formed to have a different set length each other. The length of adjacent channel waveguides 4a are different from each other with xcex94L. The channel waveguides 4a that constitute the arrayed waveguide 4 are generally disposed in multiple such as a hundred. However, in the same drawing, the number of the channel waveguides 4a is schematically depicted to simplify the drawing.
Additionally, optical output waveguides 6 are disposed corresponding to the number of signal light(s) having a different wavelength each other, the signal light(s) is (are) demultiplexed or multiplexed by the arrayed waveguide grating, for example. However, in the same drawing, the number of the optical input waveguides 2 and the optical output waveguides 6 is schematically depicted to simplify the drawing.
To the optical input waveguides 2, optical fiber(s) (not shown) on the transmitting side, for example, is (are) connected to lead wavelength multiplexed light. The light that have been lead to the first slab waveguide 3 through the optical input waveguides 2 spread by the diffraction effect thereof to enter each of the plurality of channel waveguides 4a, propagating through the arrayed waveguide 4.
The light that have propagated through the arrayed waveguide 4 reach the second slab waveguide 5 and are condensed at the optical output waveguides 6 to be outputted. The length of the entire channel waveguides 4a that constitute the arrayed waveguide 4 are different from each other. Thus, a shift is generated in the phase of the respective lights after propagating through the channel waveguides 4a, a phasefront of the lights is tilted according to this shifted amount and the positions at which the lights are condensed are determined by this tilted angle.
Therefore, the positions at which the lights having a different wavelength are condensed differ from each other, the optical output waveguides 6 are formed on each of the position at which the lights are condensed and thereby the lights having a different wavelength can be outputted from the different optical output waveguides 6 at every wavelength.
That is, the arrayed waveguide grating has the function of light demultiplexing where plurality of lights having different wavelengths are demultiplexed from the multiplexed light that is inputted from the optical input waveguides 2 and have a plurality of wavelengths different from each other.
Since the arrayed waveguide grating has the characteristic as described above, the arrayed waveguide grating can be used as an optical demultiplexer for the wavelength division multiplexing transmission. For example, as shown in FIG. 4, when wavelength multiplexed light having wavelengths xcex1, xcex2, xcex3, . . . and xcexn (n is an integer equal to or larger than 2 are inputted from one optical input waveguide 2, these lights spread at the first slab waveguide 3. Then, they reach the arrayed waveguide 4, pass through the second slab waveguide 5, are condensed at different positions according to wavelengths and enter the optical output waveguides 6 different from each other, as set forth. The lights entered to the respective optical output waveguides 6 pass through the respective optical output waveguides 6 and are outputted from the output end of the optical output waveguides 6.
An optical fiber (not shown) for outputting light is connected to the output end of each of the optical output waveguides 6 and thereby each of the lights having different wavelength is outputted. Furthermore, when the optical fiber is connected to each of the optical output waveguides 6 or optical input waveguides 2 mentioned above, an optical fiber array, for example, is prepared in which the connecting ends of optical fibers are arranged and fixed in a linear array. Then, this optical fiber array is fixed on the connecting end side of the optical output waveguides 6 or optical input waveguides 2 and the optical fiber is connected to the optical output waveguides 6 and the optical input waveguides 2.
The arrayed waveguide grating utilizes the principle of reciprocity (reversibility) of optical circuits and thereby it has the function of an optical multiplexer as well as the function of an optical demultiplexer. That is, as reverse to the FIG. 4, when a plurality of lights having different wavelength from each other is entered from each of the optical output waveguides 6, these lights pass through the propagation path inverse to that described above, are multiplexed by the arrayed waveguide 4 and are emitted from the optical input waveguide 2.
In such an arrayed waveguide grating, the wavelength resolution is in proportion to a difference in length (xcex94L) of the adjacent channel waveguides 4a that constitute the arrayed waveguide 4, as set forth. Therefore, in the arrayed waveguide grating, the xcex94L is designed large and thereby the optical multiplexing/demultiplexing of wavelength-multiplexed lights having a narrow wavelength spacing is made possible, which could not be realized by a conventional optical multiplexer/demultiplexer. For example the xcex94L is made greater, a designed wavelength spacing for multiplexing/demultiplexing is designed 1 nm or less and thereby the function of multiplexing or demultiplexing a plurality of light signals having a wavelength spacing of 1 nm or less can be served. Thus, the function of multiplexing or demultiplexing a plurality of signal lights can be served, which is needed to realize the high-density optical wavelength division multiplexing transmission.
When the arrayed waveguide grating as described above is fabricated, for example, the flame hydrolysis deposition method (FHD) is first used, and an under cladding layer and a core layer are formed on a silicon substrate one by one. Then, photolithography is applied through a photomask depicted with the waveguide configuration of the arrayed waveguide grating. Subsequently, the reactive ion etching is used to transfer the pattern of the arrayed waveguide grating on the core layer. Then, the flame hydrolysis deposition method is again used to form an over cladding and thereby the arrayed waveguide grating is fabricated.
An arrayed waveguide grating type optical multiplexer/demultiplexer of the invention comprises:
one or more of optical input waveguides arranged side by side;
a first slab waveguide connected to output ends of the optical input waveguides;
an arrayed waveguide made of a plurality of channel waveguides arranged side by side, the channel waveguides connected to an output end of the first slab waveguide and the adjacent channel waveguides having a different set amount each other;
a second slab waveguide connected to an output end of the arrayed waveguide;
a plurality of optical output waveguides arranged side by side, the optical output waveguides connected to an output end of the second slab waveguide;
separation planes separating at least one of the first slab waveguide and second slab waveguide and crossing a path of light passing through the slab waveguide;
a slide moving member for slideable moving at least one side of the separated slab waveguides along the separation planes;
a refractive index matching agent arranged on the separation planes; and
a thin film member for covering an area arranged with the refractive index matching agent.